Contents

Physical description

Yellow-backed orioles are a yellow-bodied, sexually monomorphic species. Howell and Webb (1995) note that this species tends to average 21.5 cm (8.5 in) in length from beak to tail; making Icterus chrysater a relatively medium-sized species. Exposed skin and claws are bluish-black; in adults, the bill is black, with the base of the mandible becoming bluish-grey.

Adult males display strongly contrasting yellow and black plumage. The wings, tail, shoulders, throat, and face are all black; by contrast, the back and underparts are an extremely bright yellow. Adult females closely resemble males, but yellow parts appear slightly greenish. Despite differences in plumage coloration between sexes, it is likely that this species is extremely difficult to sex in the field.

Immature yellow-backed orioles resemble adult females in overall pattern, but are greener; additionally, the flight feathers, which are black in females, are dark brown. Immature yellow-backed orioles are easily distinguished from adult females by their olive eye-line.

Geographic distribution

Yellow-backed orioles are found throughout Central America and northern South America. In particular, the species is divided into three allopatric populations. One population, designated as the subspecies I. c. giraudii, is endemic to southern Central America, and includes Nicaragua, Panama, and Colombia. The northernmost populations comprise the subspecies I. c. chrysater and I. c. mayanensis; these subspecies are found in northern Central America and in southern Mexico. Nations that have native populations of this species include Belize, Colombia, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, Panama, and Venezuela.

Habitats

Yellow-backed orioles are able to tolerate a wide variety of habitats, but prefer open, mixed pine-oak woodlands and dry scrub forest. This species has also been sighted in banana plantations. It has occasionally colonized lowland deciduous forest.

This species is usually found in regions that are less than 900 meters in altitude, though in Central and South America populations are often seen residing at elevations greater than 1000 m. The upper altitude limit for populations observed in the wild appears to be about 3 km.

Reproduction

Yellow-backed orioles are monogamous; like many species of the genus Icterus, yellow-backed orioles breed once yearly with a single mate.

The nests of this species are shallow, dangling baskets that are usually hung from the edge of a tree limb. Members of this species appear to prefer to attach nests to the tips of palm fronds (Jaramillo and Burke 1999). Nests are usually woven of fine grasses, giving them a springy texture (Wetmore et al. 1984). Nests of this species are normally hung in the canopy of mature trees that are at least seven meters in height.

The eggs of this species are whitish, with purple scrawlings that are concentrated near the broad end of the egg. The eggs are commonly marked with evenly distributed brown lines (Jaramillo and Burke 1999; Wetmore et al. 1984).

Behavior

Agonistic interactions

Yellow-backed orioles have been observed to congregate in small flocks of up to eight individuals (Wetmore et al. 1984); these flocks are probably family units, as they are composed of individuals at varying stages of maturity. This species occasionally joins mixed-species flocks that include band-backed wrens, jays, and other medium-sized orioles (Jaramillo and Burke 1999; Wetmore et al. 1984)

Communication

This species has a clear, whistling voice, with a song resembling that of spot-breasted orioles (Icterus pectoralis). The song generally consists of a series of clear notes, but it acquires a muddy, warbled quality among populations native to southern Central America (Jaramillo and Burke 1999; Skutch 1996).

Both sexes are known to sing, which appears to be common to orioles that breed in tropical climates (Price et al. 2007). Vocalizations are generally delivered from perches high in trees (ridgely and Tudor, 1989).

Jaramillo and Burke (1999) also describe other vocalizations in this species’ repertoire. The most commonly used call has been described by Jaramillo and Burke (1999) as a “nasal ‘chert’”, but other calls include a “whistling chatter” and a “nasal alarm”.

Food habits

Diet

Yellow-backed orioles are insectivorous. Their diet consists primarily of caterpillars, wasps, ants, weevils, and other arthropods. This species' diet is often augmented with bananas and may also include nectar from balsa and Heliconia (Leck, 1974).

Feeding behaviors

This species is often observed foraging in family units or in pairs (Jaramillo and Burke 1999). Insects are hunted by probing the bark of trees or the leaves of epiphytes. While foraging for nectar, this species sometimes practices "nectar robbing", puncturing the base of an unopened flower to gain access to nectar (Morton 1979)